A widely used marine power system today is diesel electric, meaning that the thrusters and/or propellers are electric driven and that power is provided by motor generator sets driven by such as diesel-engines, fuel cells, gas-turbines, dual fuel engines, etc. The most common way of doing speed control on MGS is done by a governor with setpoint adjustment from an overall Power Management System (PMS) or all done by the PMS itself The power is taken from a power plant with many consumers, where the thrusters normally being the dominant one. A high number of MGS are normally required to be connected to the power plant in order to keep a stable frequency and/or voltage in the occurrence of consumer load variations from e.g. electric heave compensation, draw-work, winch, crane and thrusters or sudden re-configuration of the distribution system. Frequency and/or voltage variations can be fatal for the power system and might lead to black-out, fallout of subsystems, and synchronization problems for generators that shall be connected to the power grid and increased fuel consumption. The offshore industry has for many years desired to reduce the number of online MGS without increased risk of frequency and/or voltage variations and potential black out, but no substantial solution has been provided for this problem. There are several benefits from reducing the number of online MGS, such as reduced NO emission, reduced sooting, reduced fuel consumption, and reduced maintenance on the engines.
Systems for handling load and power supply to compensate for variations in load are known in the field, such as exemplified in U.S.2006/111855 where power may be redirected from the thruster, e.g. to heave compensation, and U.S.2008/284369 where the power supply is controlled based on information about the torque in the motors and e.g. the signals from a dynamic positioning control system. Thus the known system are reactive in the sense that they relate to measured, already occurred, deviations, and relate to sensed power requirements, thus e.g. a simultaneous rise in the load from one or more consumers may exceed the available power increase rate and thus result in a system frequency reduction.
The proposed invention solves the problem with significant frequency and/or voltage variations when reducing the number of online MGS with use of the equipment normally installed on a vessel, as described in the accompanying claims.
The present invention thus presents ways of integrating overall predicted load changes on heavy consumers or other sudden re-configuration of the distribution system together with the speed/power/voltage control system combined with methods for predicting load variations in a way that has never been done before.
None of the known solutions address the fact that feed forwarding the predicted total load change can be used to obtain a more stable frequency and/or voltage, compared to traditional feedback compensation.